The present invention relates to a variable displacement scroll type compressor to be used, for example, as a refrigerant compressor for an automobile air conditioner and, in particular, to a variable displacement mechanism of a scroll type compressor.
Variable displacement mechanisms of scroll type compressors are disclosed in, for example, Japanese First (unexamined) Utility Model Publication No. 1-162094 and Japanese First (unexamined) Patent Publication No. 5-280476.
In the former publication, a pair of cylinders each communicating with bypass holes are provided in an end plate of a fixed scroll, and a hollow valve member is slidably-received in each of the cylinders for opening and closing the bypass holes. Opening of the innermost bypass hole is achieved by moving the valve member to a position where a hole formed at an intermediate portion of the valve member coincides with the innermost bypass hole. When the innermost bypass hole is opened, refrigerant gas is relieved to the suction side through the innermost bypass hole, the valve member hole and the hollow inside of the valve member.
On the other hand, in the latter publication, one cylinder communicating with bypass holes is provided in an end plate of a fixed scroll, and a valve member is slidably received in the cylinder for opening and closing the bypass holes. Opening of the innermost bypass hole is achieved by moving the valve member to an innermost position in the cylinder so as to pass the innermost bypass hole.
In the former publication, a diameter of the cylinder is required to be the sum of a diameter of the hollow inside of the valve member and thicknesses of the walls of the valve member. Further, it is possible that the valve member rotates in the cylinder so that the coincidence of the innermost bypass hole and the valve member hole is not guaranteed. Considering the rotation of the valve member, an annular groove communicating with the valve member hole may be necessary on the outer circumference of the valve member. Provision of the annular groove increases thicknesses of the walls of the valve member and thus a diameter of the valve member to thereby increase a diameter of the cylinder. Accordingly, the thickness of the end plate of the fixed scroll is increased to further increase the axial length and the weight of the compressor.
On the other hand, in the latter publication, only one cylinder is provided for relieving the refrigerant gas via the bypass holes while a pair of crescent-shaped sealed working spaces are formed as pressure chambers. Thus, the flow rate of the refrigerant gas through the cylinder is large to cause a large pressure loss. For lowering the required power during the reduced displacement operation of the compressor, it is necessary to reduce the pressure loss at the cylinder and thus design the cylinder with a larger bore. Accordingly, like the former publication, the thickness of the end plate of the fixed scroll is increased to further increase the axial length and the weight of the compressor.